A fuel cell utilizes a principle opposite the water electrolysis to generate electricity by causing hydrogen and airborne oxygen to chemically react. Theoretically, the only emission is water. Generally, hydrogen is used as the fuel gas and air or an oxidant gas is used as the oxygen.
As a fuel cell of this kind, for example the “fuel cell” disclosed in Japanese Patent Laid-Open Publication No. 2000-123848 is known. This fuel cell has a structure wherein a cell module is constructed by sandwiching an electrolyte film with an anode electrode and a cathode electrode and sandwiching the outer side faces of the anode electrode and the cathode electrode with a first separator and a second separator respectively by way of gaskets.
More specifically, first flow passages to become fuel gas flow passages are formed on the inner side face of the first separator, second flow passages to become oxidant gas flow passages are formed on the inner side face of the second separator, and these flow passages respectively supply fuel gas and oxidant gas to the electrolyte film in the center.
As mentioned above, because the electricity output obtained with one cell module is small, a required electricity output is obtained by making a stack of many such cell modules. The first and second separators are called “separators” because they are separating members for preventing fuel gas or oxidant gas from leaking into adjacent cells.
The first separator has first flow passages for fuel gas on its inner side face, and the second separator has second flow passages for oxidant gas on its inner side face; it is necessary for the gases to be brought into contact with the anode side electrode and the cathode side electrode effectively, and for this it is necessary for many extremely shallow grooves to be provided as the first and second flow passages.
The first and second separators each have in a top part a fuel supply opening and an oxidant gas supply opening for supplying fuel gas and oxidant gas to the first and second flow passages, and each have in a bottom part a fuel gas discharge opening and an oxidant gas discharge opening. Also, the first and second separators each have a cooling water supply opening for passing cooling water in their top part and have a cooling water discharge opening in their bottom part.
The cooling water supply opening and the cooling water discharge opening are each connected to cooling water passages. The cooling water passages are for example formed by cooling water passage grooves being formed in outer side faces of the first separator and the second separator and these cooling water passage grooves being brought together with cooling water passage grooves formed in a separator of an adjacent cell.
When the cooling water passages are formed by bringing separators together like this, a seal member for preventing the leakage of cooling water becomes necessary at the interface of the separators, and the thickness, shape and material and so on of this seal member must be considered.
Also, on one side of the first separator or the second separator gas flow passage grooves must be provided, and on the other side cooling water passage grooves must be provided, and the molding of the grooves becomes difficult.
And also, because separators are brought together, electrical contact resistance between the separators increases, and it may happen that due to this contact resistance a voltage drop arises in each cell and the output of the fuel cell becomes small.
So, when manufacturing a separator for a fuel cell, in forming the cooling water passages in the separator, it is desirable that a seal not be necessitated and that it be possible to form the cooling water passages easily, and furthermore that output decrease of the fuel cell be suppressed.